Numerous methods and devices are known for measuring temperature. For example, the mercury thermometer has existed for hundreds of years. While the mercury thermometer may be acceptable for measuring the temperature of the human body, it faces limitations in effectiveness above certain temperatures and/or under dynamic or harsh conditions. Such conditions may include the interior of an internal combustion engine or on a moving blade of a gas turbine.
A gas turbine engine is an example of a device within which extremely high temperatures and harsh conditions prevail. Gas turbine engines may be used for various purposes, including propulsion and power generation. A typical gas turbine engine includes rotating and non-rotating components, such as the compressor, combustor and turbine sections of the engine, each of which operates in a different temperature range. In the turbine section of a gas turbine engine, the turbine blades are exposed to gases which may reach temperatures of 2500° to 3000° F.
Due to corrosion, mechanical and thermal degradation concerns, it is desirable to monitor the temperature of the surfaces of rotating and non-rotating components employed in gas turbines and other devices operating under harsh conditions. A number of techniques have been used to monitor the surface temperature of blades, vanes, combustors, discs etc. in gas turbine engines, including wire thermocouples, thin film thermocouples, infrared photography, pyrometry (including 3d pyrometry), thermographic phosphors and thermal paints. A common technique used in the aircraft engine environment employs embedded thermocouple wires in the blade or vane wall. However, embedding wires in the walls may cause significant structural and aerodynamic problems, including perturbing the flow of air used to cool blades and vanes. This perturbation may affect the boundary layer of air next to the blade and may adversely impact turbine performance.
Another embedded thermocouple technique, commonly referred to as “thermal spray thermocouples,” employs plasma sprayed alumina or ROKIDE® (a registered trademark of Saint-Gobain Ceramic Materials, Latrobe, Pa.) ceramic coatings to encapsulate small diameter thermocouple wires on blades and vanes. Due to the thermal mass of the wires and associated ceramic insulator layer, such devices can introduce significant measurement error.
Infrared photography also has been used for surface temperature measurement. Infrared photography is a non-contact method in which thermal radiation patterns of an object are converted into a visible image. Such techniques are not easily transferable to the gas turbine engine environment for temperature monitoring, however, because smoke or other particulates may scatter the light. The extreme temperatures and velocities within a gas turbine engine also make it difficult to produce reliable infrared images. Pyrometry also may be used at a reasonably large distance from an object of interest in environments where the object of interest may be focused, however, the areas of the engine to be instrumented should be line-of-sight accessible. Additionally, adsorption by dust, windows, flames, gases and other optical interference can produce errors.
Yet another method to measure surface temperature is by using thermal paints. Thermal paints, also known as temperature indicating paints, provide a simple, effective and inexpensive way to obtain a visual record of the temperature distribution over the surface of components. Such paints can be applied to components having complex surface shapes, do not modify the thermal behavior of a component during testing, and can yield a visual display or thermal map of the component of interest. However, thermal paints typically exhibit poor adhesion and thus require special techniques to survive the harsh environment in gas turbine engines, such as described in U.S. Pat. No. 5,720,554 to Smith, et al., “Apparatus and method for the calibration of thermal paint.” Other types of thermal paints having better adhesion are known, such as those described in Gregory et al, “Method of Preparing Ceramic Coatings for Temperature Measurement,” U.S. Pat. No. 5,338,566 and Gregory et al, “Ceramic Coatings for Temperature Measurement,” U.S. Pat. No. 5,135,795.
Thermographic phosphors also have been used to measure the surface temperature of turbine engine components. Thermographic phosphors rely on measurements of the rate of decay of the fluorescent response of an inorganic phosphor as a function of temperature. Once calibrated over a temperature range of interest, the phosphor is excited with a pulsed laser and the fluorescent decay is measured to calculate the temperature of the substrate. In many instances, only a small amount of material needs to be deposited onto the surface to provide an adequate fluorescent signal. Suitable phosphors are available to cover a wide range of temperatures and many of them are oxide ceramics that can withstand extremely high temperatures.
It is desirable to measure the temperature of the turbine blades while in operation, since such information is important to monitoring integrity of the blade for safety and maintenance reasons. The need for accurate surface temperature measurement becomes increasingly more important as operating temperatures in gas turbine engines are pushed to higher levels. Previously-known temperature measurement apparatus, however, are not ideal for use in measuring the temperature of an operating turbine blade for a number of reasons.
Thermocouples have been used for many years as temperature measurement sensors and continue to be developed for use in harsh environment. For example, U.S. Pat. No. 7,582,359 to Sabol et al., describes a common strategy for measuring temperatures on turbine blades by placing thermocouple sensors and connections (electrical leads or fiber optics) in “trenches” formed within a turbine vane. U.S. Pat. No. 3,006,978 to McGrath et al describes the use of thin film thermocouple conductors, U.S. Pat. No. 4,665,276 to Elbel et al describes a thermoelectric sensor and U.S. Pat. No. 4,779,994 to Diller et al describes a heat flux gage. As the heat resistant coating on the blade erodes, however, the trenches may become exposed and compromise the structural integrity of the blade. In addition, the relatively large thermal mass of the connectors and any associated insulation may introduce significant error in the measured temperatures.
While it has been proposed to attached thermocouple devices to a turbine blade using adhesives, the high temperatures, high velocities of gas impinging on the turbine blade and acceleration forces caused by rotation of the turbine vanes can make such methods of attachment problematic. In addition, although the thin film sensors may be non-intrusive, in that the sensor thickness is considerably less than the gas phase boundary layer thickness, such sensors still may suffer from limitations associated with providing trenches or other features needed to connect the sensors to the associated monitoring equipment.
Another disadvantage of previously-known sensing systems is the need for external power to sense and report temperatures. For example, U.S. Pat. No. 6,622,567, describes a system having a strain gage including a differentially variable reluctance transducer coupled with an RFID device, in which an external reader transmits energy to the device to enable the strain measurement, and communicate that measurement to the reader. Similarly, U.S. Pat. No. 7,474,230 to Blom et al describes a system in which an RFID tag is coupled to a battery that powers a part of the circuitry of the RFID tag, including an RF communication block for receiving and transmitting RF signals. A sensor block including a frequency ratio digitizing temperature sensor alternately measures the ambient temperature and the voltage of the battery employed for the performing measurements.
J. H. Lin et al., “Wireless temperature sensing using a passive RFID tag with film bulk acoustic resonator”, IEEE Ultrasonics Symposium, Volume 2, Issue 5, pp. 2209-2212 (2008), describes a passive RFID tag gathers power via inductive coupling from RF power for temperature sensing. The frequency of the oscillator varies with the temperature linearly in the range of 10 to 80 degrees Celsius at 2.48 GHz, thus enabling temperature to be determined by measuring the shift of oscillation frequency. However, the device described in that article is not suitable for use in a gas turbine environment. Similarly, G. Bergmann, et al., “Multichannel Strain Gage Telemetry for Orthopedic Implants,” J. Biomechanics Vol. 21, No. 2, pp. 169-176 (1988), and C. Townsend, et al, “Remotely powered, multichannel, microprocessor-based telemetry systems for smart implantable devices and smart structures,” Proc. SPIE, Vol. 3673, 150 (1999) describe strain gages that are remotely and continuously powered. L. K. Baxter, “Capacitive sensors design and Applications,” IEEE Press, 1997, describes a device employing a microcontroller which produces a train of pulses or a single interrogation pulse to excite a capacitive limit switch, however, the circuit described in that article does not explain how to measure more than the two positions of the capacitor and does not provide temperature compensation.
K. Opasjumruskit et al, “Self-powered wireless temperature sensors exploit RFID technology,” Pervasive Computing, IEEE, Volume 5, Issue 1, January-March 2006, pp. 54-61, describes a self-powered wireless temperature sensor that utilizes RFID technology in a CMOS batteryless device measures temperature and performs calibration to compensate for sensor imperfections. An RF link using passive RFID backscattering technique wirelessly transmits the data to a reading device while extracting power from the same signal, thus enabling the device to operate in a variety of environments. Wireless sensors employing CMOS transistor technology are described in Kocer et al, “An RF Powered, Wireless Temperature Sensor in Quarter Micron CMOS,” Wireless Integrated Microsystems Engineering Research Center (WIMS-ERC), University of Michigan, Ann Arbor, Mich., as well as Gerard C. M. Meijer, “Thermal Sensors Based on Transistors,” Sensors and Actuators, volume 10, pp. 103-125 (1986). None of the devices described in the preceding articles appear to be suitable for use in harsh environments such as combustion engines and gas turbines.
Y. Wang, “A Passive Wireless Temperature Sensor for Harsh Environment Applications,” Sensors, vol. 8, pp. 7982-7995 (2008) describes a wireless temperature sensor reported to be suitable for use in harsh environments. That article describes a passive LC resonant telemetry system that relies on a frequency variation output, and which is integrated with a high dielectric constant-temperature sensitive ceramic material to measure temperature without contacts, active elements, or power supplies within the sensor. The article states that the device is capable of withstanding temperatures up to 235° C., but provides no information that the device would function effectively at significantly higher temperatures, such as those found in a gas turbine engine.
US Patent App. Pub. No. 20090147824 to Schafer et al, entitled “Wireless remote passive temperature sensor for monitoring food,” also describes a passive wireless temperature sensor with a loop antenna reportedly capable of withstanding repeated exposure to temperatures of 500° F. (˜260° C.). The article provides no information whether that device would function effectively at significantly higher temperatures, such as those found in a gas turbine engine, nor does it appear that this device would be suitable for use attached to a rotating turbine blade.
V K Varadan et al, “Design and Development of a Smart Wireless System for Passive Temperature Sensors,” Smart Materials and Structures, Volume 9, No. 4, pp. 379-388 (2000), describes a passive surface acoustic wave (SAW) sensor that uses a special FM radar for transmitting and receiving FM electromagnetic signals. S. Ballandras at al, “Wireless temperature sensor using SAW resonators for immersed and biological applications”, Ultrasonics Symposium, 2002, Proceedings, 2002 IEEE, Volume 1, pp. 445-448 (2002) discusses the possibility of measuring temperature using a passive wireless surface acoustic wave device. Similarly, S. Hashimoto et al, “Design and Fabrication of Passive Wireless SAW Sensor for Pressure Measurement,” IEEJ Transactions on Sensors and Micromachines, Volume 128, Issue 5, pp. 230-234 (2008), describes the design and fabrication of a time division multiple access passive wireless pressure sensor using 2.45 GHz surface acoustic wave delay lines. None of the devices described in the foregoing references appear suitable for use in the gas turbine environment.
In view of the foregoing, previously-known temperature measurement systems and methods have a number of disadvantages which limit use of such systems in gas turbine engines and other harsh environments.
In particular, there exists a need for a temperature measurement system and methods wherein the sensor is sufficiently thin so as to not significantly effect the boundary layer of an operating turbine blade, but is sufficiently durable to withstand the extreme thermal and mechanical environmental conditions encountered in such applications.
It further would be desirable to provide temperature measurement systems and methods having a small footprint, mechanical mass and robust mode of attachment, so as not to introduce undesirable vibrational modes in the blades.
Additionally, it would be desirable to provide temperature measurement systems and methods having a small thermal mass so as not to obscure the actual surface temperature measurement, and which is capable of rapidly responding to temperature changes.
It still further would be desirable to provide temperature measurement systems and methods that exhibit high availability when employed in a gas turbine environment, and that avoid the need to provide a power supply on a rotating portion on the turbine.
It is also desired to provide temperature measurement systems and methods which provide a high degree of discrimination such that temperature changes are translated into a measurable quantity having sufficient magnitude that temperatures can be accurately determined.
It is further desired to provide temperature measurement systems and methods with the ability to communicate temperature measurements to another region, such as outside of a gas turbine engine.